1. Field of the Invention
This invention relates to a method for stabilizing the activity of catalysts used in the conversion of hydrocarbons. More particularly, it pertains to a method for reducing the aging rate of hydrodewaxing catalysts employed in either distillate dewaxing or lube dewaxing processes.
2. Description of Related Art
This invention is concerned with processes used to reduce wax content of hydrocarbon fractions by conversion of straight or slightly branched paraffin hydrocarbons. Such processes may utilize shape-selective dual function catalysts in the presence of hydrogen, a technique which is known as catalytic hydrodewaxing.
It is known in the art to add olefins to a hydrocarbon oil cracking process in order to produce products of improved quality. U.S. Pat. No. 3,758,400 to Hampton describes a method of cracking hydrocarbon oils in the presence of an aromatic concentrate containing olefinic hydrocarbons in order to produce gasolines of increased octane number. U.S. Pat. No. 3,954,600 to Gladrow et al. relates to a method for increasing yield and selectivity to middle distillate boiling range components in the catalytic cracking of a hydrocarbon feedstock by conducting said cracking in the presence of a normally liquid olefin-containing naphtha. U.S. Pat. No. 4,146,465 to Blazek, Sr. et al. relates to a process for increasing the octane rating of gasoline and decreasing the quantity of coke produced by a catalytic cracking process by adding C.sub.2 to C.sub.6 linear olefins to the gas oil feed. U.S. Pat. No. 4,181,597 to Yan et al. discloses a process for improving the stability of a hydrocracked mineral oil by reacting the oil with an olefin stabilizing agent in the presence of a heterogeneous acidic catalyst.
In addition to the above methods, it is also known in the art to utilize olefins in the alkylation of waxy hydrocarbons to normally liquid hydrocarbons. For example, U.S. Pat. No. 4,176,044 to White discloses a process for alkylating normally solid hydrocarbons to liquid hydrocarbons boiling primarily in the lube oil range, by contacting the wax and a low molecular weight olefin, such as ethylene, with a catalyst comprising one or more C.sub.3 -C.sub.5 carbon atom secondary alcohols at elevated temperatures and pressure.
The prior art also describes certain methods for stabilizing the activity or controlling the aging of acidic crystalline zeolite catalysts used in hydrodewaxing. For example, U.S. Pat. No. 4,247,388 describes a method for controlling the aging of such catalysts by adjusting their initially high acid activity to lower levels by methods such as steaming or ion exchange.